The present invention relates to dental amalgam compositions.
The dental amalgams are prepared by tritulating alloy powders composed mainly of silver and tin with mercury, and condensed and set into the cavities of the teeth in the mouth.
In what follows, all the percent refers to % by weight unless otherwise noted. Heretofore, the alloys for the dental amalgam have been composed mainly of silver, 65% min., tin, 29% max., mercury, 3% max., and zinc, 2% max., as specified by JIS T-6109. However, it has been found that such amalgam alloys meeting the specification have insufficient mechanical properties and corrosion resistance, since, once set, a phase of Sn.sub.7-8 Hg (.gamma..sub.2) is crystallized out, which is poor in strength and susceptible to corrosion.
Recently, it has been proposed to use the high-copper or dispersion-strengthened type of amalgam alloys which cause no crystallization of such a phase. These alloys include copper in an amount exceeding the upper limit provided by the foregoing Japanese Industrial Standards (JIS), and have been come up with to make improvements in mechanical properties by causing crystallization of Cu.sub.3 Sn (.epsilon.) or Cu.sub.6 Sn.sub.5 (.eta.) phase, while suppressing crystallization the Sn.sub.7-8 Hg (.gamma..sub.2) phase. However, these proposals have taken no care of initial compressive strength after condensation and the toxicity of the leaching mercury. In other words, it takes several hours to make the condensed amalgam reach a strength sufficient to resist biting forces; in the meantime, there is a possibility that the condensed amalgam may break due to external forces, if applied. To add to this, the conventional amalgam has another disadvantage in that, during setting, it comes in contact with oral fluids, so that the harmful mercury leaches and accumulate in the body.